1. Field of the Invention
The present invention relates to a method of forming a superconductor film composed of a compound of magnesium (Mg) and boron (B). More specifically, the ]present invention relates to a method of forming an as-grown film having a high critical temperature superconductor without being annealed.
2. Description of the Related Art
A MgB2 compound features one of the highest transition temperatures of any superconductor. Additionally, a MgB2 film can be integrated on a substrate to form an integrated circuit. Thus, the MgB2 compound is expected to apply to electronics devices such as thin film devices.
It is reported that the coherent length "xgr"(0) of MgB2 is 54, and the magnetic penetration depth is 140-180 nm. One well known method of making the superconductor of MgB2 is to form a bulk of MgB2 by compression molding of powder of mono-crystal MgB2, and then annealing the bulk at a high temperature. Another method of forming the superconductor of MgB2is to form a thin film of a MgB2 compound by using PLD (pulse laser deposition), and then annealing the thin film of MgB2 in the temperature range of 600xc2x0 C.-1200xc2x0 C. to make the film superconductive. The PLD method focuses a pulsed laser beam on a boron target to evaporate boron atoms and deposit the boron atoms on a substrate. The boron atoms on the substrate then react with magnesium atoms in high temperature magnesium vapor to form a MgB2 film on the substrate. Further, the film is annealed at a high temperature, so as to become a superconductor. Another method of forming the superconductor film of a MgB2 compound by using PLD is that which deposits magnesium and boron atoms on a substrate by laser deposition, and sets the substrate in magnesium vapor. The magnesium and boron on the substrate react in the magnesium vapor to form a thin film of the MgB2 compound on the substrate. Annealing the MgB2 film at a high temperature enables the film to have the features of a superconductor.
All prior art regarding fabrication of the superconductor of the MgB2 compound requires high temperature annealing, in the range of 600xc2x0 C.-1200xc2x0 C. The necessity of the annealing process of the MgB2 film to produce features of a superconductor makes fabrication of a device such as a thin film integrated circuit on a substrate difficult. Further, it has not been known that an as-grown film of MgB2 on a substrate which is made by simultaneous magnesium and boron sputtering, using a sputtering apparatus, has characteristics of a superconductor without annealing the as-grown film.
The present invention features a method of forming a superconductor film of MgB2 without annealing the as-grown film.
The present invention provides a method of forming an as-grown film of a superconductor composed of the MgB2 compound made with magnesium and boron ejected from a magnesium target and a boron target, respectively, in a simultaneous sputtering process. The as-grown film composed of the compound of magnesium and boron can be a superconductor without being annealed. The as-grown film can be composed of a MgB2 compound, or the film can be composed of one or more compounds of magnesium and boron different from the MgB2 compound, or a magnesium element and a boron element in addition to the MgB2 compound.
As mentioned above, a superconductor film of MgB2 made using the present invention has features of a superconductor without being annealed, and its critical temperature is in the range of about 6K-29K. The present invention can be applied to fabricate an integrated circuit of a superconductor film, because the high temperature annealing process is not needed to make the as-grown film of the MgB2 compound having features of a superconductor.
The objects, advantages and features of the present invention will be more clearly understood by referencing the following detailed disclosure and the accompanying drawings.